Process for the solvent extraction for the radiolysis and dehalogenation of halogenated organic compounds in soils, sludges, sediments and slurries

ABSTRACT

A process of extracting halogenated organic compounds, and particularly PCBs, from soil, sediment, slurry, sludge and dehalogenating the compounds contacts a contaminated soil sample with an extraction medium of a mixture of an alkane and a water miscible alcohol. The organic compounds dissolve in the extraction medium which is separated from the soil by passing water upwardly through the soil. The extraction medium floats to the surface of the water and is separated. Thereafter, the extraction medium containing the halogenated organic contaminants is subjected to ionizing radiation to radiolytically dehalogenate the compounds.

RELATED APPLICATION

This application is a divisional application of application Ser. No.09/168,894, filed Oct. 9, 1998 now U.S. Pat. No. 6,132,561.

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Application No. 60/062,820 filed Oct. 13, 1997.

The U.S. Government may have certain rights in this application pursuantto Contract No. DE-AC07-94ID13223 between the U.S. Department of Energyand Idaho National Engineering Laboratory.

FIELD OF INVENTION

The present invention relates to a process for extracting halogenatedorganic compounds, and particularly poly-chlorinated-biphenyls (PCB's)from soils, sludges, sediments and slurries, and radiolyticallydehalogenating and destroying the halogenated organic compounds withionizing radiation.

BACKGROUND OF THE INVENTION

PCB's and other halogenated organic compounds are hazardous contaminantsin soils, sludges, sediments and slurries. During the past threedecades, studies performed on the toxicological effects of thesecompounds led to a ban on the use of PCB's and a ban, curtailment, orrestrictions on the use of many other halogenated organic compounds.While the manufacture of PCB's is now prohibited in the United States,the size of the environmental burden in water, sediments, soil, disposalsites, and in electrical transformers is large. The National Academy ofSciences has estimated this burden at 1.25 billion pounds. For nearly 50years, until the cessation of production in 1977, industry manufacturedand used PCB's in the United States. The properties that made PCB'sdesirable for industrial applications, i.e., their chemical and thermalstability, as well as their non-flammability, are the samecharacteristics that make them a persistent problem in today'senvironment. The inherent thermal and chemical stability of PCBcompounds also make them resistant to acid base reactions, hydrolysis,chemical oxidation, photo-degradation, and thermal changes. Today, PCB'sare still found in electrical lighting ballasts, electricaltransformers, and capacitors manufactured before the ban of PCB's in1977. Moreover, as a result of manufacturing operations, spills and thedisposal of electrical equipment, large areas of soil and sediment arealso contaminated with PCB's. The contaminated material includessediments and sludges in harbors, waterways, wetlands, and wastewatersettling and discharge areas.

The U.S. Environmental Protection Agency has recommended a number ofalternate treatment methods for PCB's. The most widely used method isincineration. Other methods include biological treatment,solidification, vitrification, treatment with potassium polyethyleneglycolate (KPEG), solvent washing/extraction, and adsorption on granularactivated carbon. Incineration is used for PCB contaminated soil,sediment, and liquids. However, it suffers from high cost and publicresistance because of residues and stack emissions that may becontaminated with hazardous products of incomplete combustion orcombustion by-products.

Two emerging technologies that are gaining acceptance include biologicaltreatment and solvent washing/extraction. Biological treatment of PCB'sis limited to relatively low PCB concentrations, may act very slowly,and may generate hazardous treatment by-products. Also, biologicaltreatment has not been proven effective for all PCB congeners. Soilwashing/extraction must be integrated with other disposal or treatmenttechniques such as incineration or other alternative dechlorinationtechnologies such as KPEG. These techniques may have high cost and donot generally avoid the environmental and practical disadvantages ofthermal or chemical destruction methods.

Ionizing radiation, i.e., x-rays/gamma-rays, electrons, or ions, hasbeen shown to be an effective means of dechlorinating organic compounds.The chemical reactions induced by the ionizing radiation are calledradiolysis. In 1974, Sawai, Shinozaki and Shimokawa Bulletin of theChemical Society of Japan 1974, 47(8), 1889-93 reported the radiolyticdechlorination of PCB's in isopropanol and alkaline isopropanol.Subsequent investigations by Singh showed that in the presence ofionizing radiation, alkaline isopropanol solutions formed radical anionsand solvated electrons. The radical anion and the solvated electronreacted with the PCB's in solution. These reactions led to thedechlorination of the compounds. In alkaline solutions, Singh alsoreported that isopropanol anions lose a proton to form an acetone anion.The acetone anion participates in the stepwise dechlorination of PCB'sand produces acetone and biphenyls as the reaction products. Radiolyticdechlorination of PCB's in soil and oil matrices was proposed by Singhbased on his experimental results.

In 1991, Mincher et al. Appl. Radiat. Isot. 1991, 42, 1061-1066 showedthat stepwise dechlorination of PCB isomers such as 2, 2′, 3, 3′, 4, 5′,6, 6′-octachlorobiphenyl at concentrations of 42 mg/l in neutralisopropanol solution occurs at applied gamma-ray dose between 20kilograys (10 kilograys=10 kGy=1 megarad=10 joule/g absorbed energy) and100 kGy. Mincher also reported that dechlorination of Aroclor 1260 (aPCB mixture) in electrical transformer oil is similar to the mechanismresponsible for dechlorination in neutral solutions. Moreover, toxicoxidation byproducts such as dioxin and dibenzofurans are not generatedby the reduction reaction in organic solutions. Based on these results,Mincher also proposed radiolytic dechlorination as a method of PCBdestruction.

Although the radiolytic dechlorination of PCB's in solution has beenwell proven, the radiolytic dechlorination of PCB's in soil may requirelarge doses. The large doses lead to higher cost for the treatmentprocess. Although data on the radiolytic dechlorination of PCB's in soilis not presently available, recent research on dioxin (another hazardoushalogenated organic compound)contaminated soil is available. Hilarideand Gray Environmental Progress 1994, 28, 2249-58 irradiated soilcontaminated with 100 ng/l of 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD). In the presence of a surfactant (RA-40, 2%), with 25% moisture,and an applied dose of 800 kGy, approximately 93% of the TCDD wasdechlorinated. Soil contaminated with the TCDD was also irradiated inthe study. Approximately 55% of the TCDD was dechlorinated with 450 kGyof applied gamma-ray dose. Gray also reported that when electron beamswere used instead of gamma-rays or x-rays from Bremsstrahlung sources,radiolytic dechlorination was not observed.

One example of a process for the decomposition of halogenated organiccompounds is disclosed in U.S. Pat. No. 4,832,806 to Helfritch. Thedisclosed process directly irradiates the soil contaminated with thehalogenated organic compounds. This process has the disadvantage ofrequiring large doses of radiation.

Several researchers have investigated solvent washing and extractionprocesses for recovering PCBs. Such processes can be used to extract thecontaminants from the soil for radiolytic treatment of the contaminantswithout the interference of the soil provided scavengers. Kapila andClevenger, at a field evaluation in Visalia, Calif., demonstrated aninnovative soil washing flotation process for remediation of the soil ina batch process. Excavated soil containing dioxin and poly-cyclicaromatic hydrocarbon (PAH's) compounds from creosote were excavated andplaced in processing bins. An alkane-alcohol mixture in a 5:1 ratio wasthen added to the soil. The alkane used in the experiments was Soltrol170 manufactured by the Phillips Petroleum Corporation. The alcohol usedin the experiments was butanol, an alcohol with low water solubility.The amount of alkane-alcohol solution added to the soil was 28% byvolume. This filled the pores of the soil. The alkane-alcohol mixturewas floated out of the soil 12-36 hours after solvent incorporation. Theremoval efficiency for initial concentrations of 480-610 ng/kg ofoctachlorodibenzo-p-dioxin was well over 90%. Similar removalefficiencies for PAH concentrations of 630-5800 ng/kg were alsoreported. The PAH's included phenanthrene, fluoroanthene, pyrene,benzo-a-anthracene, benzo-b-fluoranthene, benzo-d-fluoranthene,chrysene, and dibenz-a-h-anthracene. Additional alkane-alcoholextractions were also shown to reduce further the concentration ofcontaminants in the soil. Once floated in water, the alkane-alcoholvolume emulsified and could be easily separated from the flotationwater. This reduced the volume of the contaminant (increased theconcentration) by a factor of three.

Overcash et al. Environ. Sci. Technol. 1991, 25, 1479-85 had also showna similar desorption process using isopropanol that could solubilizeTCDD at slightly lower equilibrium concentrations. Partitioning of theTCDD off of the soil surface into the solvent was found to occur in 2-6hours, typically, when alcohol alone was used as a solvent.

In other prior processes, the radiolytic dechlorination of Aroclor 1260in electrical transformer oil was shown by Mincher. The results ofMincher and those of Gray's experiments suggest that if the soil orsoil-like particles are not present, then the radiolytic dechlorinationprocess would proceed efficiently. Moreover, in this case, the use ofelectron beams for radiolytic dechlorination of halogenated compoundscan be economical.

In previous electron driven radiolysis practice, dose uniformity isachieved by low beam utilization or by ‘two-sided’ irradiation, i.e.,the use of two opposing accelerators. In the case of solid objects to betreated, ‘two-sided’ irradiation can also be obtained by flipping thesolid object over after treatment by an electron beam from one side andtreating the opposite side of the object. Both of these approachesresult in higher cost for treatment. Use of two accelerators at leastdoubles the size, complexity, and capital equipment cost of thefacility. Flipping the target to be treated is most commonly performedon solid targets and has not been effectively done with multi-componentliquids except in recirculating systems in which the material makes manypasses. The lack of an inexpensive and easily implemented means toobtain dose uniformity has resulted in a higher cost of treatment.Accordingly, there is a continuing need in the industry for improvedprocesses for treating contaminated soils containing halogenatedinorganic compounds.

SUMMARY OF THE INVENTION

An object of the present invention, therefore, is to provide a processfor the solvent extraction of halogenated organic compounds that iscompatible with and complementary to radiolytic dehalogenation. Thesolvent extraction process uses short chain alkanes, generally a mixtureof C₆H_(x)-C₁₀H_(x) compounds and a radiolytically advantageous or inertsolvent to desorb the halogenated compound from the soil or soil-likeparticles. The solvent is preferably a lower alcohol that is miscible inwater. Examples of suitable solvents include isopropanol, t-butanol andmixtures thereof.

A further object of the present invention is to provide a method offloating the desorbed halogenated compounds and alkane-alcohol mixtureto the top of a contaminated volume of solid particulate material thatcan include soil, sediment, slurry, or sludge so that the alkane-alcoholmixture and contaminant can be removed from the solid particulatematerial. Thereafter, the mixture containing the contaminants iscollected and subjected to ionizing radiation so that radiolyticdehalogenation of the halogenated compounds occurs.

Another object of the present invention is to provide a method forsubjecting the halogenated compounds to ionizing radiation withcontinuous mixing so that a highly uniform radiation dose is appliedwith high utilization efficiency of the radiation source's output power.

Still another object of the present invention is to provide a method forthe efficient radiolytic dehalogenation of the halogenated organiccompounds obtained by a solvent extraction/flotation method.

A further object of the invention is to provide a process of extractinghalogenated compounds, and particularly polychlorinated biphenylcompounds, from contaminated soil using a solvent extraction medium thatdoes not interfere with radiolytic dehalogenation of the halogenatedcompounds.

Another object of the invention is to provide a process fordehalogenation of halogenated compounds by directing a beam of ionizingradiation to a thin, turbulent layer of a solvent containing thehalogenated compounds.

A further object of the invention is to provide a process fordehalogenating halogenated organic compounds by subjecting the compoundsto ionizing radiation while passing the compounds through an apparatushaving an outer annular wall and a rotating inner annular wall spacedfrom the outer wall.

The objects of the invention are basically attained by providing aprocess for recovering water-insoluble organic compounds from soil,sludge, slurry, sediment material, or mixtures thereof, comprising thesteps of contacting a material containing water insoluble organiccompounds with a solvent extraction medium for sufficient time tosolubilize a substantial portion of the organic compounds into themedium and form a treated mixture, wherein the solvent medium comprisesa mixture of a liquid alkane and an alcohol that is compatible withradiolytic dehalogenation, contacting the soil mixture with a sufficientamount of water to separate a substantial portion of the extractionmedium from the treated mixture, whereby the extraction mediumcontaining dissolved organic compounds rises to the surface of thewater, and separating the extraction medium from the water.

The objects of the invention are further attained by providing a processof the in situ reclamation of water insoluble halogenated organiccompounds from contaminated ground, said process comprising the stepsof: introducing an extraction medium into a containment area surroundingby an impermeable barrier member in the ground and contacting thecontaminated ground for sufficient time to solubilize a substantialportion of the halogenated organic compounds contained therein, whereinthe extraction medium is a mixture of an alkane and an alcohol that iscompatible with radiolytic dehalogenation, thereafter introducing asufficient amount of water into the containment area to displace theextraction medium from the ground and to cause the extraction medium torise to a level above the ground, separating the extraction medium fromthe water, and subjecting the separated extraction medium to ionizingradiation and dehalogenating the halogenated organic compounds.

Another object of the invention is to provide an apparatus fordelivering a substantially uniform ionizing radiation dose to a fluid,the apparatus comprising: an outer containment tank having an outerwall, a fluid inlet and a fluid outlet; an inner drum rotatably mountedin the outer containment tank, the inner drum having a wall spaced fromthe outer wall to define a substantially annular fluid containment area;a motor for rotating the inner drum with respect to the outercontainment tank for producing an azimuthal velocity of fluid in theannular containment area; and an ionizing radiation source for directingionizing radiation into the annular containment area.

Other objects, advantages, and salient features of the present inventionwill become apparent from the following detailed description, which,taken in conjunction with the annexed drawings, discloses the preferredembodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings which form a part of this disclosure:

FIG. 1 is a flow chart showing a process of a preferred embodiment ofthe invention;

FIG. 2 is a schematic diagram of the apparatus for the ex-situ treatmentof contaminated soil;

FIG. 3 is a schematic diagram of the apparatus for the in-situ treatmentof contaminated soil;

FIG. 4 is a schematic diagram of the irradiating apparatus for inducingturbulent flow mixing;

FIG. 5 is a dose-concentration curve for determining the dechlorinationrate for Aroclor 1260 in spiked soil with an initial concentration of200 mg/kg;

FIG. 6 is a dose-concentration curve for determining the dechlorinationrate for Aroclor 1260 in spiked soil with an initial concentration of 58mg/kg;

FIG. 7 is a dose-concentration curve for determining the dechlorinationrate for Aroclor 1260 in a Soltrol 130/t-butanol flotant solution withan initial Aroclor concentration of 310 mg/kg;

FIG. 8 is a dose-concentration curve for determining the dechlorinationrate for Aroclor 1260 in a Soltrol 130/isopropanol flotant solution withan initial Aroclor concentration of 310 mg/kg;

FIG. 9 is a dose-concentration curve for determining the dechlorinationrate for Aroclor 1260 in a Soltrol 130/t-butanol flotant solution withan initial Aroclor concentration of 728 mg/kg;

FIG. 10 is a dose-concentration curve for determining the dechlorinationrate for Aroclor 1260 in a Soltrol 130/isopropanol flotant solution withan initial Aroclor concentration of 784 mg/kg;

FIG. 11 is a dose-concentration curve for determining the dechlorinationrate for an Aroclor spiked 5:1 solution of Soltrol 130 and t-butanolflotant solution with an initial Aroclor concentration of 232 mg/liter;and

FIG. 12 is a dose-concentration curve for determining the dechlorinationrate for an Aroclor spiked 5:1 solution of Soltrol 130 and isopropanolsolution with an initial Aroclor concentration of 232 mg/liter.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a process for extracting andrecovering contaminants from soil. More particularly, the invention isdirected to a process for separating halogenated compounds fromcontaminated soil, sediments, slurries and sludges and subjecting thecompounds to ionizing radiation under conditions to substantiallydehalogenate the compounds with a uniform dose.

The process of the invention in preferred embodiments contacts a volumeof soil that contains halogenated organic compounds with a solventextraction medium for sufficient time to solubilize and desorb thesoluble organic compounds in the soil. The solvent extraction mediumpreferably contains at least one component that is immiscible in water.Thereafter, a volume of water is passed through the volume of soil toseparate the solvent extraction medium from the soil. The solventextraction medium which is immiscible with the water rises to thesurface and floats on the surface of the water where it is recovered andsubjected to ionizing radiation to dehalogenate the halogenated organiccompounds.

The process of the invention is particularly suitable for treating soilscontaminated with toxic halogenated organic compounds including, forexample, polycyclic aromatic compounds, polychlorinated biphenylcompounds (PCB), and chlorinated dioxin compounds. An example of apolychlorinated biphenyl which can be removed is octachlorobiphenyl.

Referring to FIG. 1, the general process of a first embodiment of theinvention provides a contaminated material indicated in block 10. Thecontaminated material is typically a volume of soil containingenvironmentally unacceptable quantities of contaminants, andparticularly halogenated organic compounds. In further embodiments, thecontaminated material can be, for example, an absorbent material used toabsorb toxic chemicals. As used herein, the term contaminated materialrefers to any solid substrate or material including, but not limited to,soil, rock, particulate adsorbents, and particulate absorbents. The soilcan include silt, loam, sand, clay or gravel.

The contaminated material is contained within a containment areaindicated by block 12. A supply of an extraction medium mixtureindicated by block 14 is added and mixed with the contaminated materialas indicated in block 16. In preferred embodiments, the extractionmedium is a solvent formed from a mixture of an alkane and an alcohol.After sufficient contact time to allow the contaminants to desorb fromthe material and solubilize in the extraction medium, water from asource indicated in block 18 contacts the material to separate theextraction medium from the material. The water is added in a sufficientamount whereby the extraction medium floats to the surface of the wateras indicated in block 20. The extraction medium containing thecontaminants is collected as indicated in block 22 and the process wateris discharged as indicated in block 24 and the solid materials discardedas indicated in block 26. The water can be filtered and purified forreuse or discharged.

The extraction medium is then transferred to a treatment zone indicatedby block 28 and subjected to ionizing radiation indicated by block 30 todehalogenate the compounds. The extraction medium can be recirculated tothe treatment zone as indicated by loop 32 or passed to a postcollection vessel indicated by block 34. Thereafter, the extractionmedium can be further processed by filtering or other treatment toremove various compounds and recycled or discarded as indicated in block36.

The mechanism of radiolytic dehalogenation using ionizing radiation hasbeen extensively studied and those studies are well documented. Themechanism is fairly complex and is known to involve the formation ofvarious ionic species and solvated electrons which produce a chainreaction to remove the halogens from the molecules.

Experimental results of prior processes indicate that the presence ofthe soil (or similar solid particles in sediment, slurry, or sludge) mayprovide chemical scavengers that consume the solvated electrons that arebelieved to participate in the dechlorination reaction process. Thecompetition by the scavengers increases the required dose necessary todechlorinate the halogenated organic compounds at the soil surface. Thelarge doses required for dechlorination of TCDD in a soil matrix requirea large gamma-ray or x-ray source, or a very large electron acceleratorfacility for even modest TCDD concentrations and modest quantities ofcontaminated soil, sediment, slurry, or sludge.

It is further believed that the presence of the solid particles willalso limit the applicability of the radiolytic dechlorination process togamma-ray or x-ray sources rather than electron beam sources. Thislimits the applicability of radiolysis for field use (i.e., on-site andeither with excavated soil or in-situ), and where electron acceleratorsare more desirable than gamma-ray sources because accelerators can beshut off and transported while not producing radiation. For the samereasons, accelerator facilities may be easier to license and maintainthan radioactive sources.

In gamma-ray or x-ray radiation, which have high penetrating power thatcan be several centimeters or even meters, dose uniformity often isdependent mainly on the geometrical presentation to the radiation sourceof the target material to be treated. Gamma-sources generally have lowphoton utilization efficiency, but can provide very uniform dose. Also,gamma-ray sources have relatively modest dose rates of a few tens ofkilogray per hour, i.e., a few megarads per hour. In this case, thematerial to be dosed can be recirculated or stirred to further improvedose uniformity.

The prior processes which use accelerator generated electron beams asthe ionizing radiation for radiolysis typically do not provide a uniformdose to the PCBs and do not provide for efficient utilization of theelectron beam. Multi-mega-electronvolt (MeV) bremstrahlung x-ray sourcesbecome increasingly directional at higher energy, and so, can be used toprovide a more uniform dose at high dose rate. However, at energiesgreater than 10 MeV induced radioactivity poses a limitation on use, andat energies less than 10 MeV, conversion efficiency of electron power tophoton power is well below unity and dose uniformity is generally at theexpense of photon utilization efficiency. The present invention isdirected to a process and apparatus for providing uniform treatment.

In the case of multi-MeV electrons, where the penetration in oil-alcoholsolutions is in the range of only a few millimeters up to a fewcentimeters, the dose non-uniformity may be large. However, suchelectron beams with average power of up to 100 kilowatts are available.These accelerators are capable of delivering very high dose rates sothat material can receive the required dose in one pass as it flows bythe radiation field of the accelerator. In this case, the complexity ofa recirculation system can be avoided or the number of passes can besmall. Because variation of dose along the last 10-50% of the electronrange may be more than a factor of 1.5, dose uniformity is needed toobtain the most economical processing.

In the process of the invention, a volume of contaminated soil or solidparticle matrix is confined by a non-permeable barrier. If in-situ(e.g., in the ground), the barrier must extend below the contaminatedvolume and form an enclosure around the sides of the contaminatedvolume. The barrier on the side must extend above the top of the volumeso that a confined area for the extracting solvent is available abovethe ground. If the contaminated volume is to be treated ex-situ, then itmust be excavated and placed in a non-permeable container.

An alkane-solvent mixture is added to and incorporated into the volumeof contaminated soil. The amount of the solvent extraction medium addedto the soil is preferably sufficient to fill the pores and intersticesof the soil. A highly porous soil typically requires a larger volume ofextraction medium, while less porous soils may require less. Generally,the extraction medium to soil ratio is about 1:3. In-situ, the solventmixture is injected through pipes or holes made into the ground. Whenthe ground is sufficiently porous or permeable, the solvent can bepoured onto the top surface of the contaminated ground. For ex-situtreatment in the container, the solvent mixture can be poured in at thetop or introduced into the container through one or more openings at thebottom. Mixing, shredding, declumping, or maceration of the material canbe performed to enhance the dispersion of the solvent mixture throughoutthe pore volume of contaminated material.

After a suitable waiting time, typically, in the range of 1-36 hours,the halogenated organic compound will partition from the surfaces of thesolid particles into the solvent mixture. The time for this to occur canbe reduced by heating the soil and solvent mixture. Water is thenintroduced into the bottom of the volume of contaminated material.Sufficient water is added so that the solvent medium floats to the topof the contaminated soil and into the containment space above the groundso that the solvent medium can be collected.

The solvent medium is collected and placed into a container that isconnected to a treatment tank in which the solvent medium flows and issubjected to ionizing radiation. The flow can be induced either bygravity or by the action of a pump. In the case of photon radiation, thetank has a sufficiently thin wall so that it does not significantlyattenuate the radiation being applied to the solvent. In the case ofelectron or other charged particle beam, the wall has a window that issufficiently thin so that the beam of charged particles can pass throughthe window with low attenuation. The solvent can be circulated withinthe treatment tank in the azimuthal direction to provide uniformtreatment of the solvent medium. This circulation is driven by arotating cylinder situated within the treatment tank, and having an axisthat is parallel with the axis of the tank. The rate of rotation issufficiently high so that the azimuthal flow of the solvent medium has asufficiently high flow velocity and a correspondingly high Reynoldsnumber so that turbulent flow and mixing are obtained. To aid in thedevelopment of turbulence, axially oriented wires, cylinders, or vanesmay be placed in the azimuthal flow between the rotating cylinder andthe wall of the treatment tank so that separation flow occurs and avortex stream is shed by the wires, cylinders, or vanes.

The solvent is exposed to the ionizing radiation until a sufficientdegree of dehalogenation has occurred. The delivered radiation dose maybe increased by recirculating the solution through the irradiationtreatment tank. After a sufficient dose is delivered, the treatedsolvent medium is collected in another container. The treated solventmedium is disposed in a final collection container or in anothercontainer that is used for transporting the solvent medium to a disposalsite.

FIG. 2 shows the schematic diagram of an apparatus for the ex-situtreatment of contaminated material. In this embodiment, the contaminatedmaterial is placed in a non-permeable container 40, which is typicallymade of metal such as stainless steel. Container 40 has one or moreopenings 42 in a bottom wall 44 for the introduction of the extractionmedium which is pumped by a pump 46 through a pipe 48 from a storagetank 50. The contaminated material is supported on a perforated screenor false bottom 52 in the container 40 so that the extraction medium andwater can engulf the material. The components of the extraction mediumare stored in tanks 54, 56 and metered through valves 58 and 60,respectively, into the storage tank 50. A mixer 62 is used to break upthe clods or clumps and to incorporate the extraction medium into thematerial when treating materials with low permeability or materials thatare prone to clod or clump formation. The mixer 62 is also beneficialfor porous and highly permeable materials.

In preferred embodiments of the invention, the extraction medium is amixture of an alkane and an alcohol. The preferred alkane is a mixtureof short chain hydrocarbons C₆H_(x)-C₁₀H_(x) such as SOLTROL™ 130manufactured by the Phillips Petroleum Company. The preferred alcohol isisopropanol because it is miscible in water, and it has a high yield inthe radiolytic reactions that constitute stepwise dehalogenation ofhalogenated organic compounds. Isopropyl alcohol has been found to be aneffective solvent for PCBs, and does not interfere with the radiolysis.Moreover, it is believed that the isopropyl alcohol produces certainanions which can assist in the dehalogenation of the halogenated organiccompounds with minimal scavenging of the solvated electrons. T-butanolcan also be used and is found to be inert during the radioloysis ofAroclor 1260. In preferred embodiments of the invention, the alcoholcomponent is a lower alcohol that is miscible in water and hassufficient solvency to dissolve or solubilize the various contaminantsand particularly, the PCBs. Preferably, the alcohol is compatible withthe radiolytic dehalogenation reaction and is sufficiently miscible sothat at least a portion of the alcohol is extracted into the water asdiscussed hereinafter in greater detail. It is believed that most of thealcohol used to desorb the contaminant is extracted by the flotationwater so that the contaminant is dissolved primarily in the alkane. Theratio of the alkane to the alcohol can vary depending on the alcohol,the porosity of the soil being treated and the particular compoundsbeing extracted. Generally, the alcohol to alkane ratio is about 1:5,but can range from about 1:10 to about 9:10.

Further improvement in the subsequent radiolysis may be obtained byusing an alkaline-alcohol solution. The alcohol is made alkaline by theaddition of sodium hydroxide or potassium hydroxide. A suitable amountof sodium hydroxide or potassium hydroxide is added to the alcohol toraise the pH by one or two and to provide a sufficient number of sodiumor potassium ions in the alcohol that remains in the flotant after theextraction process. The chloride ions produced during the radiolysiswill react with the sodium or potassium ions and precipitate from theextraction medium. The removal of the chloride from the extractionmedium during radiolysis improves the radiolysis process reactionkinetics by reducing competition reactions.

After the alkane-alcohol mixture is contacted with the contaminatedmaterial for a sufficient period of time, typically 1-36 hours, toeffect the partition of the contaminant into the extraction medium,flotation water is pumped into container 40 by pump 64 through a pipe 66from a storage tank 68 or other water supply. Thealkane-alcohol-contaminant mixture will separate from the solid materialand float to the top of the water. Sufficient water must be introducedinto container 40 so that the layer of the extraction medium is abovethe top surface of the solid materials in container 40 and can bereadily separated from the water. As the extraction medium is brought tothe top surface, it is removed by draining or by pumping via a pump 70through a pipe 72 into a collection tank 74.

During or after the collection of the extraction medium in tank 74, someof the medium may be removed by draining or by a pump 76 and carriedthrough pipe 78 to a treatment tank assembly 80. As the medium passesthrough the treatment tank assembly 80, ionizing radiation indicated byarrows 82 produced by at least one radioactive source or chargedparticle accelerator 84, preferably a multi-MeV electron accelerator, isdirected into the medium through window 86. The ionizing radiationsource can be any suitable source as known in the art, such as electronbeam, ion beam, x-ray, gamma ray and photon sources. The applied dose ofthe ionizing radiation during the dehalogenation process is about 1 toabout 1000 kilogray. The ionizing radiation source can be, for example,a Co-60 or Cs-137 source, as well as other sources capable of inducingradiolytic dehalogenation.

After dosing the extraction medium as it flows through the treatmenttank assembly 80, the extraction medium can be recirculated, ifadditional dose is needed, by pump 88 through exit/recirculation pipe 90so that it can be reintroduced into the treatment assembly 80. A numberof valves 92 are situated on the input pipe 78, exit/recirculation pipe90, and an output pipe 94 so that the flow can be directed to thedesired location. After a sufficient dose is applied, the material flowsthrough the output pipe 94 to a collection tank 96 and ultimately to acontainer 98 for disposal.

FIG. 3 is a schematic diagram of the process and apparatus for in-situtreatment of contaminated material 100 that has not been excavated, andremains in the ground. In this arrangement, the material 100 issurrounded by a non-permeable barrier 102 that also extends above thesurface of the ground of the contaminated material. The barrier 102preferably extends upwardly a distance to form a containment area 101 tocontain extraction solvent and water. The barrier can be a naturalimpermeable material such as dense clay or rock. Alternatively, thebarrier can be a prepared material such as grout, metal plates,concrete, plastic sheets, rigid panel, or other materials. The barriercan also be formed by injecting water in the soil that is a frozen inplace by pipes carrying refrigerants or by injecting cooling fluid.Barrier members can be put into place by excavation and backfillingtechniques, by drilling and insertion, or by impact insertion. Thebarrier 102 is embedded into the ground to define an encircled area tocontain the extraction medium. The barrier 102 is generally embedded toa depth at least equal to the depth of contamination and preferably adepth below the contamination to allow efficient contact of thecontaminated soil without the extraction medium leaching into thesurrounding areas.

In the embodiment illustrated in FIG. 3, barrier 102 is shown asextending under the contaminated soil of the containment area. Thebarrier under the containment area can be applied by known techniques,such as, for example, extruding a grouting material. In soils where animpermeable layer, such as clay or rock, lies below the contaminatedsoil, it is often not necessary to place a barrier along the bottom ofthe containment area.

After the barrier 102 is in place, one or more pipes 104 are insertedinto the soil within the containment area of the barrier 102. The pipes104 are inserted into the soil to a depth at least equal to the depth ofthe contamination. An extraction medium is injected under pressure froma supply pipe 106 through injection pipes 104 into the soil in asufficient amount to dissolve or solubilize the contaminants in thesoil.

In embodiments of the invention where the contaminated soil issufficiently porous and permeable, the extraction medium can be appliedto the surface of the ground and allowed to percolate downwardly intothe soil. Holes (not shown) can be drilled or dug into the soil and theextraction medium injected into the holes and allowed to percolate intothe soil by gravity or under applied pressure.

As in the ex-situ process, the extraction medium is introduced into thecontaminated soil material and allowed to contact the soil for a periodof several hours. Once sufficient partitioning of the contaminant off ofthe solid particle surfaces has been achieved, water is introducedthrough the pipes 106 and 104 into the soil. A sufficient amount ofwater must be added to fill the containment area whereby the extractionmedium rises to the surface of the soil within the containment area.

Once the extraction medium emerges at the surface, it is removed by pump110 via pipe 112 and collected in a tank 114. During or aftercollection, extraction medium is drained or pumped by pump 116 throughpipe 118 and carried to a treatment apparatus as in the ex-situarrangement.

Referring to FIGS. 2 and 4, the treatment apparatus 80 includes acontainment tank 130 having an outer wall 132. Containment tank 130 isgenerally made of aluminum or stainless steel. In the preferredembodiment, containment tank 130 has a substantially cylindricalconfiguration having an axial length L and a radius (b). Outer wall 132typically has a substantially circular shape. In further embodiments,outer wall 132 can have an oval or non-circular shape. Containment 1stank 130 is closed at each end by end walls 134 and 136 which arecoupled to side wall 132 to define a containment area 138. End wall 134includes an inlet opening 140 for receiving the extraction mediumthrough an inlet pipe 142. End wall 136 includes an outlet opening 144for discharging treated extraction medium to an outlet pipe 146, In theembodiment illustrated, the inlet opening 140 and outlet opening 144 arecoaxially aligned. In alternative embodiments, the inlet opening 140 andoutlet opening 144 can be offset from each other. The dimensions of thecontainment tank can vary as desired. A suitable containment tank has aradius of about 51 cm.

Treatment apparatus 80 further includes an inner drum 148 that isdimensioned to fit within containment tank 130 and to be freelyrotatable therein. Inner drum 148 is made of suitable materials such asaluminum or stainless steel and includes a substantially cylindricalinner wall 150 and end walls 152 and 154 coupled to inner wall 150.Inner drum 148 has a radius (a) and a length slightly less than thelength of containment tank 130. A suitable radius for inner drum 148 canbe about 50 cm. In preferred embodiments, inner drum 148 is completelyclosed to prevent liquids from entering the inside of inner drum 148. Infurther embodiments, inner drum 148 can be non-cylindrical, butpreferably rotates about a common center axis with containment tank 130.

Inner drum 148 is provided with an axial shaft 156 coupled to end wall152 and an axial shaft 158 coupled to end wall 154. Axial shaft 156 ismounted in a fluid-tight bearing 160. Axial shaft 158 is mounted in afluid-tight bearing 162 and is coupled to a drive motor 164 for rotatingthe inner drum 148 about its center axis within containment tank 130.

Window 86 is provided in outer wall 132 of containment tank 130. In thepreferred embodiments, window 86 extends substantially the entire lengthof outer wall 132 and has a width sufficient to permit the ionizationbeam to enter the containment tank 130. Window 86 is a suitable materialof a thickness to be permeable to the ionizing radiation to allow theradiation such as an electron beam to be transmitted into the treatmentapparatus. In one embodiment, window 86 is a thin metal foil having athickness significantly less than the electron penetration range.Examples of a suitable window is titanium or stainless steel foil havinga thickness of about 2 to 200 micrometers for a multi MeV electron beam.

In use, the extraction medium is introduced into a reaction zone 166formed between the outer wall 132 and the inner drum 148 in the regionadjacent to window 86. Rotation of the inner drum 148 causes theextraction medium to flow in a substantially spiral path from the inlet140 to the outlet 146. Turbulent mixing in this spiral flow ensuresuniform exposure to the ionizing beam.

For a given electron beam average power P (in kilowatts) and a requiredionizing radiation dose D, typically 20-100 kilogray and dependent onthe initial and desired post treatment concentrations of contaminant,the quantity of material M that can be treated in an hour with beamutilization efficiency U is given by the following equation.$M = {3.6 \times 10^{6}\left( \frac{PU}{D} \right)}$

Typically, the utilization efficiently U is 50% or more. The requiredionizing radiation dose is about 20-100 kilogray, although the dose canvary depending on the initial concentration of the contaminants in themedium and the desired final concentration levels. For a 10 kW beam with50% utilization, a 100 kilogray dose can be delivered to 180 kg ofcontaminated extraction medium per hour. If the material mass density isapproximately unity, i.e., 1 g/cc, then 180 liters per hour can betreated.

The inner drum 148 has an outer radius a and the outer wall 132 has aninner radius b, so that the depth of the annular reaction zone 166 isb−a. In preferred embodiments, the inner wall is concentric with theouter wall 132 to provide an annular reaction zone of substantiallyuniform depth or thickness. In further embodiments, the inner drum canbe eccentrically mounted with respect to the containment tank 130 sothat the reaction zone 166 has a non-uniform depth. In preferredembodiments, the depth of reaction zone 166 is approximately equal tothe electron penetration range in the extraction medium. Typically, thedepth is about one centimeter for a 2 MeV electron beam. The reactionzone in the area exposed to the ionizing radiation is about 0.1 to about10 cm, and preferably about 1 cm. For an apparatus where a is 50centimeters, and b is 51 centimeters, the reaction zone has a crosssectional area of 317 square centimeters. For a flow rate of 180 litersper hour, this corresponds to an axial flow velocity of 0.16 cm persecond. An apparatus having a length L=50 cm, the material has aresidence time in the apparatus of approximately 300 seconds.

Turbulent mixing of the extraction medium in the reaction zone requiresthe Reynolds number, R, for the flow to be greater than 10,000. TheReynolds number is given by $R = \frac{lu}{v}$

Where l, u, v are the scale length, azimuthal velocity, and viscosity,respectively. In preferred embodiments, a plurality of vanes 170 arecoupled to the outer wall to induce turbulence in the flow. Vanes 170are generally a planar member positioned in the containment zone 138about midway between the outer wall 132 and inner wall 150. The vanescan be suspended by brackets coupled to the outer wall or coupled to endwalls of the containment tank. Alternatively, a plurality of wires,cylinders or baffles are positioned in the containment zone 138 toinduce turbulence. Typically, et l≈1 cm for vanes or wires, 170,arranged axially along the gap to induce vorticity and generateseparated flow. The viscosity is approximately 0.02 sq cm per second forthe flotant. To obtain a sufficiently large Reynolds number, e.g.,15,000, it is necessary for u to be greater than 300 cm per second. Thiscorresponds to a rotational frequency of 60 rpm when a is 50 cm. Thiscan easily be accomplished with a commonplace motor with a rating of afew horsepower. The power necessary to rotate the inner drum can bedetermined using standard calculations as disclosed in L. D. Landau andE. M. Lifshitz, Fluid Mechanics, Eddison Wesley, Reading, Mass., pp.60-61 (1959) and A. Sommerfeld, Mechanics of Deformable Bodies, AcademicPress, NY, N.Y., p. 253-262 (1950).

With this apparatus, the slow axial flow is rapidly spun in theazimuthal direction, and turbulent mixing is induced by the rotation ofthe inner drum. The portion of the extraction medium that received asmaller dose because it was near the end of the electron penetrationrange is mixed and carried to other radial positions in the reactionzone so that it receives various ionizing radiation doses as it movespast the window. In this manner, the dose is averaged for each elementof the fluid.

In the practical application of the process, it is useful to know thedose-constant so that the amount of dose D that is necessary to reducean initial concentration C₀ to a desired post-treatment concentration C.The initial and post-treatment concentrations are related by thefollowing equation:

C=C ₀ exp{−γD}

where γ is the dose-constant. If the dose is given in megarads, then thedose-constant has units of 1/megarads.

EXAMPLES

The following is a description of tests performed with Aroclor 1260 todetermine the dose-constant for treatment of PCB by theflotation/extraction and radiolysis process. FIGS. 5-12 showdose-concentration curves for test samples 1-8. The reduction inconcentration as dose increases can be fit to an exponential functionand the dechlorination rate (dose constant) can be determined. Theresults of these tests are summarized in Table I. The dose-constant isgiven by: $\gamma = {\frac{1}{D}{\ln \left( \frac{C_{0}}{C} \right)}}$

TABLE I Test Results Initial Aroclor 1260 Dose constant Test SampleConcentration (1/(megarad)) 1. Spiked soil 200 mg/kg 0.011 +/− 0.001 2.Spiked soil 58 mg/kg  0.016 +/− 0.0025 3. Flotant/Soltrol/t-butanol 310mg/liter 0.413 +/− 0.108 4. Flotant/Soltrol/isopropanol 310 mg/liter(ppm)  0.44 +/− 0.020 5. Flotant/soltrol/t-butanol 728 mg/liter 0.242+/− 0.034 6. Flotant/Soltrol/isopropanol 784 mg/liter 0.176 +/− 0.027 7.Spiked Soltrol/t-butanol 232 mg/liter 0.194 +/− 0.047 8. SpikedSoltrol/isopropanol 232 mg/liter 0.202 +/− 0.007

In the these tests, gamma radiolysis was performed using a Co-60 sourcelocated at the University of Missouri—Columbia's research nuclearreactor. The Co-60 used was a composite source comprising two weak andtwo strong sources. Dose rates of 3.1 to 5.7 megarads per hour weredelivered. The dose was measured with calibrated radiochromic filmFWT-60 purchased from Farwest Technology in Goleta, Calif. Theradiochromic film was made into dosimeters and were calibrated at 0.50,1, 3, and 10 megarads.

Several clean soil samples were spiked with 100 mg/kg and 300 mg/kg ofAROCHOR™ 1260 obtained from Fisher Scientific dissolved in iso-octane.Several of the spiked soils were mixed for 24 hours using a tumbler andthen allowed to set for 24 hours. A Soltrol 130 solvent solutioncontaining either 20% isopropanol or 20% t-butanol was added to the soiland allowed to equilibrate for 24 hours. Following the equilibrationperiod, distilled water was pumped upwards through the soil. The Soltrol130 alcohol mixture was collected and transferred to a reaction vessel.

After irradiation, liquid samples were diluted 1:500 with hexane andanalyzed directly using gas chromatography (GC). A gas chromatographusing a computerized peak and quantification program was used in theanalysis. Hexachlorobenzene was used as an internal standard during theanalysis. Spike recoveries ranged from 80-120%.

Several of the spiked soil samples were subjected to ionizing radiationwithout attempting to extract the Aroclor 1260. The initialconcentration of the soil and the results of the dose are shown in Table1.

The amount of Aroclor 1260 remaining in each sample after a specificdose was determined and subtracted from the initial amount to measurethe amount of dehalogenation and destruction of the PCB. Directseparation of the Aroclor 1260 from the spiked soil sample was notpossible without liquid extraction because of interference from thesoil. Soil samples were placed on a column containing 5 g of sodiumsulfate, 20 ml of acid silica gel and 5 g of sodium sulfate. Twentymilliliters of methylene chloride was added to the soil sample andallowed to diffuse through the soil samples into the column. After onehour, the extract was slowly drained from the column. The column wasrinsed with 10 ml of methylene chloride, and the solution collected.Three milliliters of hexane and 0.2 ml of Soltrol 130 were added to thesoil.

The extract-Soltrol-hexane was rotary evaporated, leaving the Aroclor1260, hexane, and Soltrol. The samples were then diluted to a finalvolume of 10 ml using hexane. The aliquot was analyzed using the gaschromatographic procedures described above to determine the amount ofAroclor remaining in the soil sample after each dose.

The summary of the tests is given in Table 1. The floated solutionscontaining Aroclor 1260 had the highest dose constant. This indicatesthe highest rate of dechlorination of the samples tested. Analysis ofthe tests show that the radiolytic dechlorination of Aroclor 1260 in thetest sample observe first order rate kinetics. In all of the test data,a plot of the natural logarithmic decomposition rate vs absorbed dosewas found to be linear, which indicates first order rate reaction. Theslope of the curve is the dose constant. The higher the dose constant,the more efficient is the dechlorination process.

FIGS. 5-12 show the concentration vs dose curves for the various testsamples 1-8. It is seen that a dose on the order of 100 megarads (1000kGy) is necessary to obtain a modest reduction in the PCB concentrationin the spiked soil samples. In contrast, when the Aroclor is desorbedfrom the soil surface and then extracted using the flotation process ofthe invention, the dose constant and efficiency increases by up to afactor of 40. The flotation process removes the Aroclor from the soiland reduces the scavenging of the solvated electron. At higherconcentrations it is found that the dose constant is less than at lowconcentrations. This suggests that the rate of dechlorination has aconcentration dependence and decreases as the concentration increases.

In both the Soltrol 130 t-butanol tests and the Soltrol 130-isopropanoltest, 30% by volume of the Soltrol—alcohol solution was added to thesoil. Following flotation, approximately 75-80% of the Aroclor 1260 wasremoved from the soil in a single flotation. Mass balance also indicatedthat 80-85% of the Soltrol-alcohol solution added to the soil wasrecovered after flotation. This indicates that the alcohol in theSoltrol-alcohol solvent partitions into the flotation water. Within theresolution of the analysis, the process was found to concentrate theAroclor 1260 by a 3:1 volume in the flotant as calculated. This suggeststhat the flotation process is also a candidate for volume reduction ofcontaminants at remediation sites.

For comparison, tests were made with Soltrol solutions of the twoalcohols in a 5:1 concentration that were spiked with Aroclor 1260.These solutions were not exposed to soil. As seen in Table I, the doseconstants for these tests were approximately a factor of two lower thanfor the flotated solutions.

In iso-octane, and alkane similar to Soltrol 130, both geminate andsolvated electrons were found to participate in the radiolyticdechlorination of the PCB's this is believed to account for theconcentration dependence in dechlorination vs dose. In neutralisopropanol, the electrons become solvated, however, and thedechlorination rate is independent of PCB concentrations. In the spikedSoltrol-alcohol solutions, the process is mixed and competition kineticssuggests that the presence of an alcohol can compete for radiolyticallygenerated electrons. This is consistent with the observed test results.In the floated solution, the alcohol is believed to be scavenged by thewater used for flotation, thereby leaving behind the Aroclor 1260 andthe Soltrol 130. When the flotant is irradiated, the reaction kineticsare similar to that of an iso-octane solution. However, when a spikedsolution containing Aroclor 1260 in a Soltrol 130-alcohol solution isirradiated, the polar alcohol in solution solvates the radiolyticallygenerated electrons, decreasing the efficiency of the reaction and thuslowering the dose constant. This suggests that a flotation process thatuses an alcohol miscible in water is more efficient than a flotationprocess that uses an immiscible alcohol.

Although various embodiments have been selected to demonstrate theinvention, it will be understood by those skilled in the art thatvarious modifications can be made without departing from the scope ofthe invention as defined in the appended claims.

What is claimed is:
 1. A process for separating water-insoluble organiccompounds from a soil, sludge, slurry, sediment material, or mixturesthereof, comprising the steps of: contacting a material containing waterinsoluble organic compounds with a solvent extraction medium forsufficient time to solubilize a substantial portion of said organiccompounds into said medium and form a treated mixture, wherein saidsolvent medium comprises a mixture of a liquid alkane and an alcohol,said alcohol being compatible with radiolytic dehalogenation; contactingsaid soil, sludge, slurry, sediment material or mixtures thereof with asufficient amount of water to separate a substantial portion of saidextraction medium from said treated mixture, whereby said extractionmedium containing dissolved organic compounds rises to the surface ofsaid water; separating said extraction medium from said water; whereinsaid alcohol is isopropyl alcohol, t-butanol or mixtures thereof.
 2. Aprocess for separating water-insoluble organic compounds from a soil,sludge, slurry, sediment material, or mixtures thereof, comprising thesteps of: contacting a material containing water insoluble organiccompounds with a solvent extraction medium for sufficient time tosolubilize a substantial portion of said organic compounds into saidmedium and form a treated mixture, wherein said solvent medium comprisesa mixture of a liquid alkane and an alcohol, said alcohol beingcompatible with radiolytic dehalogenation; contacting said soil, sludge,slurry, sediment material or mixtures thereof with a sufficient amountof water to separate a substantial portion of said extraction mediumfrom said treated mixture, whereby said extraction medium containingdissolved organic compounds rises to the surface of said water;separating said extraction medium from said water; wherein saidextraction medium comprises a C₆-C₁₀ alkane and isopropyl alcohol in aratio of about 1:10 to about 9:10.
 3. A process for separatingwater-insoluble organic compounds from a soil, sludge, slurry, sedimentmaterial, or mixtures thereof, comprising the steps of: contacting amaterial containing water insoluble organic compounds with a solventextraction medium for sufficient time to solubilize a substantialportion of said organic compounds into said medium and form a treatedmixture, wherein said solvent medium comprises a mixture of a liquidalkane and an alcohol, said alcohol being compatible with radiolyticdehalogenation; contacting said soil, sludge, slurry, sediment materialor mixtures thereof with a sufficient amount of water to separate asubstantial portion of said extraction medium from said treated mixture,whereby said extraction medium containing dissolved organic compoundsrises to the surface of said water; separating said extraction mediumfrom said water; contacting said soil with an amount of said extractionmedium to substantially fill a pore volume of said material.
 4. Aprocess for separating water-insoluble organic compounds from a soil,sludge, slurry, sediment material, or mixtures thereof, comprising thesteps of: contacting a material containing water insoluble organiccompounds with a solvent extraction medium for sufficient time tosolubilize a substantial portion of said organic compounds into saidmedium and form a treated mixture, wherein said solvent medium comprisesa mixture of a liquid alkane and an alcohol, said alcohol beingcompatible with radiolytic dehalogenation; contacting said soil, sludge,slurry, sediment material or mixtures thereof with a sufficient amountof water to separate a substantial portion of said extraction mediumfrom said treated mixture, whereby said extraction medium containingdissolved organic compounds rises to the surface of said water;separating said extraction medium from said water; wherein saidextraction medium further contains sodium hydroxide, potassiumhydroxide, or mixtures thereof.
 5. The process of claim 4, comprisingcontacting said extraction medium with said material for about 1-36hours.
 6. The process of claim 5, wherein said halogenated compounds areselected from the group consisting of polychlorinated biphenyls,chlorinated dioxins, and mixtures thereof.
 7. A process of the in situseparation of water insoluble halogenated organic compounds fromcontaminated ground, said process comprising the steps of: introducingan extraction medium into contaminated ground in a containment areasurrounded by an impermeable barrier member in the ground and contactingsaid contaminated ground for sufficient time to solubilize a substantialportion of said halogenated organic compounds contained therein, whereinsaid extraction medium is a mixture of an alkane and an alcohol that iscompatible with radiolytic dehalogenation, thereafter introducing asufficient amount of water into said containment area to displace saidextraction medium from said ground and to cause said extraction mediumto rise to a level above said ground, and separating said extractionmedium from said water.
 8. The process of claim 7, further comprisingpositioning said impermeable barrier member in the ground to define saidcontainment area.
 9. The process of claim 8, wherein said barrier is aplastic sheet or rigid panel embedded into the ground.
 10. The processof claim 8, comprising injecting a cooling fluid into the ground tofreeze water in said ground to form said impermeable barrier.
 11. Theprocess of claim 8, further comprising the step of excavating an areaaround said contaminated area, positioning said barrier in saidexcavated area, and backfilling said excavated area to retain saidbarrier in place.
 12. The process of claim 7, comprising injecting saidextraction medium into said ground to a depth at least equal to a depthof said contaminated ground.
 13. The process of claim 7, comprisinginjecting said water into said ground to a depth at least equal to thedepth of said contaminated ground.
 14. The process of claim 7, whereinsaid alcohol is selected from the group consisting of isopropanol,t-butanol and mixtures thereof.
 15. The process of claim 7, wherein saidalkane is a mixture of C₆-C₁₀ alkanes.
 16. The process of claim 7,wherein said extraction medium comprises a C₆-C₁₀ alkane and isopropylalcohol in a ratio of about 1:10 to about 9:10.
 17. The process of claim7, comprising contacting said ground with an amount of said extractionmedium to substantially fill a pore volume of said material.
 18. Theprocess of claim 7, wherein said extraction medium further containssodium hydroxide, potassium hydroxide, or mixtures thereof.
 19. Theprocess of claim 7, comprising contacting said material with saidextraction medium for about 1-36 hours.
 20. The process of claim7,wherein said halogenated compounds are selected from the groupconsisting of polychlorinated biphenyls, chlorinated dioxins, andmixtures thereof.